text:
Can a pilot fly past their 12 hour "Regularly Scheduled Duty Day" of 135.267(c) if they stay within the legal 14 hour max limit?
Can a pilot who is assigned a regularly assigned duty day under .267(c) of 12 hours, be assigned a flight on the 12th hour (right before they would normally go home) which would cause the pilot to fly in their 13th hour of Duty? (Below the legal maximum 14 hour duty limit)
Background info:
I am looking to learn more about .267(c). The internet does not seem to hold much information on it, except that many believe it is a schedule that almost no one uses.
Many folks interpret 135.267(c) as the permission to exceed flight times in .267(b), and while that is true, it is within a context of a different crew schedule, called the "Regular Scheduled Duty Day".
From “Berry 2009” FAA Legal interpretation:

Certificate holders may establish flight crew member schedules under
the "moving 24 consecutive hour" flight time limitations of §
135.267(b), or the regularly assigned duty period of no more than 14 hours flight time limitations of § 135.267(c). - “Ross 1993”

While it does not explicitly say it, .267(c) is meant to resolve the issues of the rolling 24 hour flight time limitations, under specific circumstances.  While crew members may not exceed the same daily flight time (8 hours single pilot), they can exceed the 8- in-24.
Ex.  Pilot flies 8 hours from 10am to 6pm on Monday, then on Tuesday, starts flying at 8am.  This would exceed the 8-in-24, but if it is during a regularly scheduled duty day under .267(c) this is perfectly legal.
"Regularly assigned duty day” is defined as:

“comes to work and… goes home at the same time every day” - “Berry
2009”
"regularly assigned duty periods are not intended to be implemented
for short periods of time." - “New 2013”
“A schedule of at least four weeks a reasonable amount of time to
establish a regularly assigned duty period." - “New 2013

From “Berry 2009”:
Hypothetical Regularly assigned duty period of 0600-1800

"If the 'day' pilot who began his 'availability' at 0600 was
'notified' for a flight assignment at 1600 and reported to the
airport, what is the latest time he can operate an aircraft under FAR
Part 135 without violating section l35.267(d)? Should he be concluded
by 2000 (14 hours from 0600), or can he operate the aircraft until
0600 the next morning (14 hours from the time he was 'notified')?"
“This answer assumes the hypothetical company is operating single
pilot flight crews. In this situation, because the flight crew
operates under a regularly assigned duty day, the provisions of 14
C.F.R. § 135.267(c) apply. Under section 135.267(c), a regularly
assigned duty period may not exceed 14 hours. Section 135 .267(d) does
not apply in this situation because it pertains to unscheduled part
135 operations not using regularly assigned duty periods. Accordingly,
the pilot in your hypothetical must conclude flight time by 2000 hours

14 hours from the start of his regularly assigned shift. See Legal Interpretation 1993-21 (Aug. 30, 1993). Note that although 14 hours is
the maximum length of a regularly assigned duty day prescribed by
regulation, operators, such as the one in your hypothetical, may elect
to use a shorter duty day.”

The question above indicates that the person asking the question is confused about how all the different parts of 267 work together, including that (d) does not apply to (c).
However, although the regularly assigned duty day is 0600-1800, which is less than 14 hours, the FAA does see that the pilot is allowed to fly to 2000 (the legal limit of 14 hours of duty).  Which means the pilot did not go home at 1800, like they normally do.
Do you have experience using .267(c)?  If so, please state so in your responses.  Thank you.

I think if they were at home spending time with the family and just making sure they were near the phone and didn’t get called until 1600 and then maybe didn’t arrive at the airport and report in until 1700 then their duty time starts at 1700.   I think a regularly assigned shift includes reporting for duty and maybe hanging around the break area while waiting for an assignment.  But regularly assigned duty does not include lounging by the pool at home waiting for a call even if you are “on-call”.

Thanks for you response Jim.  FAA legal interpretation makes it clear that "on-call" is on duty, and where you spend the time (at the pool, or in the break room) does not factor into that.  However, I will not go into that further, as it does not pertain to my question.

hmm ok.  I read the FAA’s def of duty period “Duty period means the period of elapsed time between reporting for an assignment involving flight time and release from that assignment by the certificate holder. The time is calculated using either Coordinated Universal Time or local time to reflect the total elapsed time.”  where it says “reporting for an assignment”  ...

Maybe it’s my understanding of “on-call” that’s defective.

Yes, you have found the definition of duty that continues to confuse operators to this day.  The definition of "rest" is needed to further understand where Duty comes into play, because you cannot be resting, if you are on duty, and you cannot be on duty, if you are resting.  However, there are many FAA legal interpretations that further clarify this.  Since you're asking, I have provided a link below to one of them.  https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/Data/interps/2009/Berry_2009_Legal_Interpretation.pdf

This one might actually be clearer.   https://www.faa.gov/about/office_org/headquarters_offices/agc/practice_areas/regulations/interpretations/Data/interps/2009/Mayors_2009_Legal_Interpretation.pdf

They may be bureaucrats but they aren't all stupid, they know companies abuse loopholes.
The USDOT (of which the FAA is a branch) also has different categories of rest. (Explicitly used in trucker regulations. Possibly ships and trains too.) Simply being off of the clock is not sufficient for certain definitions. One type of rest logged is only valid if during a continuous period while physically in sleeping quarters and not on call, so time eating dinner or traveling to/from the hotel wouldn't count.  So even if not FAA explicit, there is common law to consider in the definition of rest.


text:
"w/o DME" minimums on DME required approach
I've found this ILS-Y 26 EPBY approach, where there are two LOC minimums: With D3.0 and w/o D3.0 on Jeppesen chart. On the original AIP charts it says "When stepdown fix not received", but how could we possibly not receive the stepdown fix on LOC (only) approach, if DME is required? Both stepdown fix as well as recommended altitudes table are based on BYD, and there's no reference to BYZ on the final approach?

It appears to me that DME is required for the localizer approach.  It is required to identify the FAF and the MAP turn back to the VOR.  It also seems to be required to correctly fly the CDFA procedure.  My only thought is if the DME fails inside the FAF, we could continue and change minimums and try to get radar vectors on the miss.

@757toga https://www.ais.pansa.pl/aip/pliki/EP_AD_2_EPBY_6-1-3_en.pdf

@wbeard52 Radar vectors are unavailable at this airport, as it is procedural TWR controlled.

Could this have something to do with using GPS in lieu of DME? Then the with or w/o part would refer to having this point stored in the DB.

DME is required equipment for the approach procedure, but note that the LOC DME minimums only apply to the Localizer DME functioning.  The missed approach holding pattern references the VORTAC DME, and not the Localizer DME.  If the Localizer DME is out you cannot identify the LOC step down fix on the FA segment, but this does not mean the approach is not flyable. The MAP can be identified by using a constant groundspeed and clock method but this method will require increased minimums for (I presume) reasons of safety.

The approach is an ILS or LOC procedure, which means you are able to fly it if you are receiving the localizer and the glideslope (ILS) or if you are receiving the localizer only (LOC). A localizer does not have DME capability, so there are minimums published if you cannot identify I-BYD D3.0. (ILS DME information comes from the glideslope's location, generally speaking, but it is separate from the glideslope guidance—so it may still be working even if the glideslope is out, or it may not be.)
The procedure requires DME in general because the missed approach has you flying to the point BY633 before turning around and holding at BYZ VOR. The point BY633 is identified as the BYZ 255 radial at 4.7 DME. You need DME to identify it.

The LOC here on 109.1 does have a paired DME, as shown in the oval with course, freq, morse code, etc. I'm not seeing a way to identify the MAP without DME from the LOC, because the timing is from another LOC DME fix. Puzzling question.

The fact that the DME is paired with the LOC freq doesn't mean anything; the DME antenna (from what I can see of the tiny diagram) is co-located with the GS antenna, as is standard. Both the DME freq and the GS freq are paired off the LOC but they are separate units. Your point about identifying the MAP is much harder to explain away...

Consider LOC only approach. You say, that for LOC approach itself you don't need DME , the requirement is there because it's needed for BY633. How do you identify FAP without DME then, and how do you perform the CDFA?

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text:
Do SIMulator hours need to be logged?
I was wondering if there is any regulation, EASA or ICAO, in other words “where does it say” that SIM hours need to be in your logbook? I’ve never recorded those, I’m going to try and upgrade my CPL to an ATP and once before I heard one guy wondering about those whilst going through my logbook. I have over 4000 hrs on the A320 family(yes, I took my time with the ATPL, it’s shameful, I know), so I have plenty of hours: cross-country, night, PICUS, all of those. But the SIM hours… Regarding evidence of training - the local authority have my file with all my records, they’ve been issuing and reissuing my licence from the very begining of my flying days. So they do have proof and can see for themselves that I have been properly trained and I have been current since I got my type rating. I would be willing to argue about those SIM hours missing from my logbook, but I’m not sure weather I had any ground. Thank you.

I can't speak for EASA.  In the US, there is no requirement that simulator hours are logged.  However, if you are going to use those simulator hours towards a rating, they must meet 2 conditions.  They (a) must have been performed in an approved simulator that meets the required BATD/AATD standards, and (b) must be recorded by "a reliable method" either in a paper or electronic logbook.  Your instructor verifies your logbook when they endorse you for the check ride, and the DPE again verifies them during the check ride.  You would never be permitted to claim unrecorded hours in the US.

Thank you. That is one of the reasons I was asking - I don’t need to use those hours for anything, I have plenty of real ones.

You only need to log hours that you plan to use for some purpose: currency, meeting requirements for a rating, or something similar.  There's no general (*) requirement that you have everything logged where you can get in trouble for not having logged some event -- in the sim or the aircraft.
The (*) on that statement comes when regulations limit how much flying one can perform in a specified period (last 7 days, last 28 days, last 360 days, a calendar month, a calendar year, etc).  In that case, you or somebody does have to log your flights, so that you or your airline can demonstrate that you aren't exceeding any limit.  That's something that airlines tend to track very carefully, and it's not left to the pilot alone.  And, in any case, the limits on flight hours and Flight Duty Period (USA - FAR Part 117) apply to actual flight hours, not simulator hours.  (Yes, hours spent in the sim are hours on duty and not in rest, but classroom time is also, and as long as the scheduling system shows adequate periods of rest, nobody cares, from a crew rest/crew duty standpoint, what fraction of the day was spent in the sim vs in the briefing room.)
If you don't need the sim hours, there's no need to reconstruct them.

Thank you. I hope hope our local CAA will see it the same way.

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text:
How long can an ELT run before the battery is dead?
I recently learned that ELTs are required to run a maximum of 60 minutes before the power supply battery has to be recharged or replaced.  This really doesn't seem like a great amount of time for this device to operate in order to facilitate locating by search and rescue crews.  I would have said a more reasonable figure would be around 24 hours.  Is it really true that ELTs are only effective for such a short period of time?

The 406Mhz ELT's are picked up by the Cospas-SARSat satellites and sent to a dispatch center with the location (5km accuracy without GPS, 100m with GNSS) so they don't need to run a long time. The older 121.5/243Mhz models used to be monitored by the same system but are no longer monitored.

The reference you quote is correct as it defines the "useful life" of the battery.  that is: if you use it for more than 1 hour (that would include the cumulative test time) it must be recharged or replaced before being returned to service.  But that isn't what you are asking about.  You are asking for the duration of operation.
The requirement for Duration of Operation is 24 hrs.
RTCA DO-204A, MOPS for 406 MHz ELTs, states

1.5 Operational Goals
b. Operability
(1) The technical requirements of the 406 MHz beacon radiated signal
  are based on the COSPAS-SARSAT system.
(a) The 24-hour operating life requirement (§2.2.1) is based upon the
  maximum COSPAS-SARSAT system waiting time, the number of satellite
  overpasses required to optimize the beacon location solution and
  battery capacity limitation at low temperatures.

and

2.2.1 Duration of Operation
Refer to COSPAS-SARSAT document C/S T.001.

and from C/S T.001

4.5.1 Duration of Continuous Operation
The minimum duration of continuous operation shall be at least 24
  hours* at any temperature throughout the specified operating
  temperature range.
The minimum duration of continuous operation for an ELT(DT) to meet
  the ICAO GADSS requirement at any temperature throughout the specified
  operating temperature range shall be 20† hours.

You're misinterpreting a section of FAR 91.207.
That regulation says, in part:

c) Batteries used in the emergency locator transmitters … must be replaced (or recharged, if the batteries are rechargeable) —

When the transmitter has been in use for more than 1 cumulative
  hour; or

. . .

This does not say the ELT/battery only has to operate for one hour, it says that if the ELT has been transmitting for one hour you must replace the battery, even if it's still perfectly good.
The one hour period is cumulative and includes the required annual ELT tests (91.207 paragraph D) and any accidental or incidental activations from a hard landing, inadvertently bumping the panel switch, etc.
This battery replacement requirement exists to ensure that the ELT will be able to function properly in a real crash & will transmit for at least the amount of time it's supposed to.
Per COSPAS/SARSAT specifications new 406MHz ELTs are required to be able to transmit continuously for a minimum of either 24 or 48 hours (depending on the type of beacon).
I believe the older 121.5 MHz ELTs also have a 24-hour continuous transmission requirement.

Edit: Damn, I type slow. 3 other (and better) answers were posted while I was typing.

I think the premise of your question is not quite accurate. The only thing "required" (within this context), is that the battery must be recharged or replaced IF it has been transmitting for 1 cumulative hour. That does not really imply that an ELT battery is only "required" (i.e. there is a regulation somewhere) to operate for at least one hour.
An ELT transmitter might have been in use for 1 cumulative hour for several possible reasons, the most likely of which is accidental triggering, or bench testing it multiple times. I've been involved in several ramp searches because a random ELT was going off in a parked, unoccupied, plane.
The FAR that applies is 91.207.  Paraphrased as:

No person may operate a U.S.-registered civil airplane unless... there
  is attached to the airplane an approved automatic type emergency
  locator transmitter that is in operable condition. Batteries used in
  the emergency locator transmitters must be replaced (or recharged, if
  the batteries are rechargeable) when the transmitter has been in use
  for more than 1 cumulative hour; or When 50 percent of their useful
  life (or, for rechargeable batteries, 50 percent of their useful life
  of charge) has expired, as established by the transmitter
  manufacturer.

So, if the ELT has been (or did) "go off" for at least one hour, the plane may not be operated until the ELT's battery is replaced or recharged.
Other documentation:

TSO-C126 describes requirements for the newer 406 Mhz ELTs.
TSO-C91 describes requirements for the older, 121.5 Mhz ELTs.
RTCA Document No. DO-188 describes the technical aspects of the batteries that must be used... type (lithium, etc.), ventilation requirements, mounting requirements, etc....
RTCA DO-204A (no public link that I could find) specifies a 24-hour continuous operation capability

I presume you are referring to this FAR.
§91.207   Emergency locator transmitters.

(c) Batteries used in the emergency locator transmitters required by
  paragraphs (a) and (b) of this section must be replaced (or recharged,
  if the batteries are rechargeable)—
(1) When the transmitter has been in use for more than 1 cumulative
  hour; or
(2) When 50 percent of their useful life (or, for rechargeable
  batteries, 50 percent of their useful life of charge) has expired, as
  established by the transmitter manufacturer under its approval.

If you read it carefully you will notice that it doesn’t say that they have a maximum life of 1 hour. Just that they must be replaced if they have been in use for more than 1 hour. This only applies to TSO C91 (121.5MHz) ELTs. The 406Mhz batteries have different lifetimes.
Getting information on how long they must transmit is surprisingly hard. Many of the technical documents cost money to access, e.g. DO-204A, Minimum Operational Performance Standards (MOPS) for 406 MHz Emergency Locator Transmitters (ELTs) so I can’t read them.
I found one reputable source for the lifetime once activated.

"Depends on a lot of factors. The design criteria is that they
  transmit for at least 48 hours at 0-degrees, some will transmit much
  longer if the weather is warm, the battery fresh, etc. Or they will
  transmit for less if it's colder, if the battery hasn't been replaced
  when it was supposed to, etc." --Richard A. De Castro -N6RCX NREMT SAR
  Tech

http://pansar.voices-inc.com/ELT.htm

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text:
What classes of aircraft require hydraulic flight controls?
All commercial airliners such as the Boeing 737 or Airbus A320 or heavier aircraft require an hydraulic system that can power actuators, which generate the required forces to move the control surfaces in all phases of flight. Smaller General Aviation aircraft do not need this.
But what about aircraft in between? Is there a minimum MTOW above which aircraft are required to or generally have an hydraulic system? Can you make examples of lighter aircraft which have it?
For example I was wondering about the an aircraft like the 19-passenger commuter Beechcraft 1900:

Required by whom? Are you asking if it's an actual regulatory requirement or something else?

@DavidRicherby Edited for clarity

The Beech 1900 uses cable controls, not hydraulics, for flight controls. The exception would be the rudder boost which is used in emergencies. I also know that the DC-9 series, including the MD-88/90, uses cable controls, but I don't know if they are boosted. I also don't know what regulation, if any, regulates this matter.

Hm. Are the only control systems used control cables attached directly to stick or hydraulics? Are there inbetween fly by wire systems that use electric winches on the control cables or some kind of electric actuator on the control surface directly?

@StarWeaver There are many possibilities. The 737 for example features mechanically linked flight controls, which are assisted by hydraulic power. The principle of fly-by-wire systems is to decouple the stick/horn from the control surface, so what you suggest is contradictory. Electric actuators are also used, as opposed to hydraulic ones. Fly-by-wire transmits the control input, hydraulics or electric actuators provide the power to move the surfaces.

@mezzanaccio Ah, cool. I didn't mean to suggest systems that were only partially fly-by-wire; I was just curious if there were any other FBW systems between the presented dichotomy of fly-by-cable and FBW/hydraulic. (Also now I'm curious about the etymolgy of 'horn', as in my mostly-spaceflight mostly-non-realistic sim and reading-about-airplanes history i've only ever heard 'stick' variants.)

@StarWeaver sorry what I meant was yoke... I lived too long in Germany.

@mezzanaccio Ah yeah I do know that one. Tho now i'm imagining some fancy texan's cessna with a custom yoke that is largely made out of bull hornsW

I don't see how your edit addresses my question at all. Again, are you asking about regulatory requirements or matters of engineering?

@DavidRicherby And I do not see how you cannot understand the question. It is simple: big A/C have hydraulics. Small ones do not. Which A/C in between do (example)? Are there explicit regulatory requirements? Yes or no.

The repeated use of the word "require"-- as well as the suggestion that you are looking for a specific numerical value for a MTOW threshold-- and the use of the word "class" which is word that has regulatory significance-- suggests that this may be a question about regulations. (And several of the answers seemed to have assumed that it was.) It would be clearer if you simply added a sentence saying "This is not a question about regulatory requirements, just about what has been found to be necessary during the actual design and flight testing of aircraft." Or something to that effect. –

Wait a minute now I see your last comment says you are asking both about regulatory requirements and practical requirements.  I know it's an old question but it would sure be clearer if had asked in two parts a) are there regulatory requirements and b) if not, in actual practice where is the threshold where hydraulic control systems have been found to be necessary -- or something like that--

@StarWeaver - “a custom yoke that is largely made out of bull horns” - That actually does not sound like a bad idea. Maybe from a Brangus with matching Longhorns on the cowl. How much drag penalty would that incur?  Just yoking.

Hydraulic flight controls are not mandatory for a specific class, but above some size and speed it will be hard to fulfil all certification requirements without at least adding some hydraulic boost.
Historically, aircraft used manual controls. With increasing size and speed, the forces went up and increasingly clever force reduction systems were invented to keep stick forces within limits.

On the first flight of the Messerschmitt Me-321 glider it was found that control forces especially in roll were way too high, so a second pilot with a second stick was installed.
The Dornier Do-335 or the Republic P-47 used a telescopic stick: At low speed the stick was short and could move through the full range of aileron deflections while at high speed it could be telescopically extended. This limited the motion range but improved the leverage of the pilot.
The English Electric Canberra used internal balances for the ailerons and a spring in the aileron controls to limit the stick forces. At top speed the control horn could still move through its full range but the achievable aileron deflections were only a few degrees - still enough for sufficient roll agility, however.

Ailerons have mass. There is a spring. Something that moves. Every engineer should think next: What about flutter? With more complex force reductions, the chance grew that something unexpected happens and failure modes multiplied. In the end, introducing hydraulics solved so many problems that de facto above a certain speed and size combination no other option makes sense.
I have worked together with Rockwell (formerly North American) on a two seat jet trainer; a size and speed combination that would have had manual controls 60 years ago. I proposed to use the same force reduction mechanisms that were used on the F-86, but in the end a hydraulic boost was selected. Why?

Nobody had any experience with manual controls anymore. After so many years, all F-86-era engineers were long retired or had passed away.
The North American archives had been thrown away years before, so no documentation was left on how to properly design a manual control system for that speed range.
The hydraulic boost system was easy to install, used standard components and was cheaper to design because everybody was familiar with the technology.

As I said before: Don't get me started on how exactly you can tailor roll stick forces - this will be a post that will be much longer than anything I have written here before.

Peter! I look forward to reading your memoirs! will you write a book? -NN

@nielsnielsen To be fair, I think the memoirs of the guy who made inkjet printing viable will be a much more interesting read. And if you take together my many answers, there is not much left to tell.

@OMG Peter how did you find that out????????????

@nielsnielsen I have my ways … :-)

@nielsnielsen It was back then when your profile picture showed you with a guitar. I was intrigued and checked out your web pages where I found a link to a document which described what you did at HP.

As far as I know there is no hard regulation requiring hydraulics at a certain point. On one hand the aircraft need to actually be controllable so if that would be unattainable at operational speeds then hydraulics would bee needed.
In the FAA's Brief on flight controls

As aviation matured and aircraft designers learned more about
  aerodynamics, the industry produced larger and faster aircraft.
  Therefore, the aerodynamic forces acting upon the control surfaces
  increased exponentially. To make the control force required by pilots
  manageable, aircraft engineers designed more complex systems. At
  first, hydromechanical designs, consisting of a mechanical circuit and
  a hydraulic circuit, were used to reduce the complexity, weight, and
  limitations of mechanical flight controls systems.

The FAR's list the limits of force on a control input in FAA FAR 23.397

(a) In the control surface flight loading condition, the airloads on
  movable surfaces and the corresponding deflections need not exceed
  those that would result in flight from the application of any pilot
  force within the ranges specified in paragraph (b) of this section. In
  applying this criterion, the effects of control system boost and
  servo-mechanisms, and the effects of tabs must be considered. The
  automatic pilot effort must be used for design if it alone can produce
  higher control surface loads than the human pilot.

Keep in mind this does not require hydraulics outright but if you can not build a cable/trim tab system that falls within these force limits you will need to add in some kind of assistance.

"uneatable"? Autoincorrect malfunction?

I get hungry when I fly sometimes, with to much control surface force I cant eat.... See correction ;)

@JonathanWalters My question was also about part 23 aircraft. The Beechcraft 1900 is a part 23 aircraft. I guess if it does not have hydraulics then no part 23 aircraft does.

@mezzanaccio Thats part of my point, but my comment wasn't clear.

There isn't a particular weight or size class for requiring hydraulic flight controls. The requirements are for control forces to stay within certain bounds, and in general this becomes more difficult with increasing size and speed of the aircraft.
Keeping the control system manual has the advantage that the aeroforces are fed back to the pilot, and that with increasing airspeed the controls stiffen up, making it harder to making large deflections which would impose high accelerations on the airframe. But larger/faster aircraft require larger control surfaces, with the associated larger control forces. However the control forces must remain within the boundaries of human force ability.

Many of the older hydraulically actuated aircraft have some form of feedback of aircraft velocity. The 737 has q-feel in the pitch channel: an artificial feel system stiffens up the flight control as a function of dynamic pressure as sensed by the pitot tube. The DC-10 and the L-1011 have this as well.
In a previous life I used to contract for simulator modelling of flight control systems of fixed wing and helicopter flight controls, and the Beech 1900 is one of the types that I worked on. It has a fully manual control system, all aeroforces are fed back to the pilot. The pitch channel has a down spring of about 40 lbf, which is apparent from ground measurements. Have heard comments about the pitch forces being high during landing, and that particularly female pilots can have trouble exerting these forces during landings. Hydraulic actuation may make it easier to fly the aircraft and tailor the required forces. There are larger and faster aircraft certified for manual control, the F100 is one: pitch has manual backup.

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text:
Why is there no alternative mechanism to extend and lock the landing gear in case of failure?
As we know, most passenger planes have redundant systems in case of failure of a mechanism. For example, in case of failure, that specific thing can be operated by another alternative method, mechanism, or a manual way. So, is there any alternate mechanism that works and can help to extend and lock the landing gear in case of failure?
I have read that landing gear can be extended by their own weight and get locked into position in case of failure of the hydraulics. What if extended gear are unlocked, but can not be retracted in order to utilize their falling weight to re-lock them into place?
We have seen situations where landing gear did not get extended and the plane needed to land on its belly. That is very dangerous for passengers. And, it can damage the plane heavily.
So, why is there not an alternate means by which you can extend landing gear that can prevent this situation. Or, maybe I am just not aware of it.

"situations where landing gears not get retracted and the plane needs to land on its belly" I'm sorry, what? if the gear is not retracted, the airplane cannot physically land on the belly, there is a non-retracted gear in the way. did you mean extended?

I am talking about this kind of situation.

so yes, you meant "not extended", not "not retracted"

According to the Wikipedia article (https://en.wikipedia.org/wiki/LOT_Polish_Airlines_Flight_16), there was an alternative mechanism, however that too wasn't working (although it would have been very easy to get it working again): "Later investigation indicated a popped circuit breaker just to the right of the F/O at floor level would have enabled the electric motor for releasing the undercarriage. The breaker was reset after landing and the undercarriage extended normally."

I have read that landing gears can be opened by its own weight and get locked into its position in case of failure of hydraulics. That is the alternative mechanism...

This question is confusing. It is going back and forth between the premises of asking if such mechanism exists and stating that there is no such mechanism.

I think the issue here is that you've asked a question based on an assumption that is not sound.  The only modern aircraft in operation that I'm aware of that do not have an alternative way to lower and lock the landing gear are craft with fixed gear or seaplanes.  I can't find any examples of aircraft which do not have at least two methods to lower the gear.  Perhaps you can provide some specific aircraft to help the validity of your question?

In transport category aircraft there has to be an alternative mechanism to extend the gear if the normal mechanism fails, but there is no requirement for an alternative retraction mechanism. This is required e.g. by EASA CS-25 (Certification Specifications for Large Aeroplanes):

(c) Emergency operation. There must be an
emergency means for extending the landing gear in
the event of –

Any reasonably probable failure in
the normal retraction system; or

The failure of any single source of
hydraulic, electric, or equivalent energy supply.

(EASA CS-25.729 - Landing Gear - Retraction Mechanism)
A common solution to implement this alternative extension is via gravity. There is usually a way to mechanically release the up-locks and shut off any hydraulics to the gear from the flight deck, which will result in a gravity gear extension, e.g. in the Boeing 737:

2 Manual Gear Extension Handles
Right main, nose, left main – Each landing gear uplock is released when related
handle is pulled to its limit, approximately 24 inches (61 cm).

(Boeing 737 NG FCOMv2 14.10.3 - Landing Gear - Controls and Indicators)
The reason why no alternative retraction mechanism is required, is that there is simply no need for it. Should the gear fail to retract after takeoff, the pilots can just land again, either at their departure airport or somewhere else (possibly after burning / dumping some fuel if the aircraft is above its maximum landing weight). Continuing the flight to the destination is usually not a good idea because the landing gear extended results in a large increase in drag and therefore requires significantly more fuel (see e.g. Hapag-Lloyd Flight 3378).
In the accident you linked (LOT Flight 16), the alternate gear extension mechanism was also unavailable due to a tripped circuit breaker:

On Dec 18th 2017 the PKBWL released their final report concluding the probable causes of the accident were:

Failure of the hydraulic hose connecting the hydraulic system on the right leg of the main landing gear with the center hydraulic system, which initiated the occurrence.

Open C829 BAT BUS DISTR circuit breaker in the power supply circuit of the alternate landing gear extension system in the situation when the center hydraulic system was inoperative.

The crew’s failure to detect the open C829 circuit breaker during approach to landing, after detecting that the landing gear could not be extended with the alternate system.

(avherald.com, emphasis mine)
The alternate landing gear extension in the Boeing 767 (as used by LOT 16) is also a gravity extension, but unlike the 737 the up-locks are released electrically rather than mechanically from the flight deck:

Landing Gear Alternate Extension
The alternate landing gear extension system uses an electric motor to trip the
locking mechanism for each gear. Selecting DN on the ALTN GEAR EXTEND
switch releases all door and gear uplocks. The landing gear free-fall to the down
and lock position.

(Boeing 767 FCOM 14.20.2 - Landing Gear - System Description)

Pull a handle 24" out of the floor of the cockpit of the 737? There's no forgetting to reset that, then, is there?

@FreeMan There are actually cables connected to those handles and they retract back inside the floor after you pulled them and the up-locks are released. You can see them in action in this YouTube video at 6:15.


text:
How often do GA pilots use the Autopilot approach feature while landing?
While flying in simulations, I found that using the Approach feature is very beneficial for riding the glide slope (clear weather or not), however, while watching videos of GA pilots, I do not see it performed too often. Which brings me to my question as to whether that is a common practice, or if it is frowned upon unless it is necessary for a safe landing?

In those videos, how many of the aircraft have autopilots installed?

touché..  I cannot say for sure, but assuming a pilot did have it installed, would it be considered common practice to do so?

First, what percentage of GA aircraft even HAVE autopilots?  In 40+ years of flying, I don't think I've ever even been in a plane (other than as an airline passenger) that had one.

How interesting would the videos be if the pilots let the AP do all the work? And how many critical comments would they get about it? Were they in VMC, where is relatively easy, or IMC, which has a much higher pilot workload?

@StephenS: good point, there's potentially some sample bias: youtube videos aren't necessarily representative of what an average GA pilot does.

Perhaps you could clarify your "student pilot" status?  I took that to mean "before getting your PPL", but most of the answers/comments seem to assume that you are doing practice instrument approaches.

@jamesqf, lots of GA planes have autopilots. My small 4-seater has one, they are not that expensive to put in.  Mine only controls the ailerons, for a few thousand more I could have had one that controlled pitch as well.  I am still hand flying my approaches for practice, one of these trips I will let the autopilot follow the Localizer, or the GPS, in calm weather, and see how well it does. Then try it in rougher weather, see what it's limitations are.

I think the use autopilot in GA would remove a great part of the fun.

@Manu H: Yes, and then a great many of my flights involve landing at airports (or other places) that don't have an ILS.  But GA is a large category, so I'm sure there are many people who only fly between larger airports.

@ManuH Some GA pilots fly for fun; others fly to places that are fun. I’m in the latter camp, so I hand-fly only enough to maintain proficiency in case the AP breaks, which does happen disturbingly often.

It's a perfectly acceptable practice, provided you disengage the autopilot upon reaching minimums and hand fly it the rest of the way.  Some manufacturers, like Cirrus, recommend flying a coupled autopilot approach.
I won't sit on the fence about this.  Learning how to fly coupled autopilot approaches are fine, but I insist all my students learn how to hand fly approaches, both as part of their initial instrument training and for all instrument proficiency checks I administer.  If I were an examiner I would insist on seeing instrument applicants demonstrate hand flown approaches on their checkrides as well.
Autopilots are great but their use can begin to atrophy their flying skills and it can come back to bite them, particularly in an emergency.
As to the exact numbers of GA pilots who fly coupled autopilot approaches, that's probably going to depend on the pilot and the equipment in his/her aircraft.  Pilots with autopilots installed are probably going to be much more likely to use them and be more comfortable flying approaches this way.

Why disconnect the autopilot at minimums? Why not disconnect at the minimum altitude certified by the AP manufacturer?

If it’s specified in the AFM, sure.

At least where I trained, DPEs require one approach flown to minimums on autopilot if your plane is equipped with one. The others (and the hold) must be hand-flown.

The question as it currently stands in the headline "How often do GA pilots use the Autopilot approach feature while landing?" is hard, if not impossible to answer due to lack of relevant statistics.
As for the matter(s) raised in the body of the question, is and should the autopilot be used on approaches in GA, here's how I see it, plain and simple:

You must be able to fly the plane manually, no matter what the situation is.
You should be able to fully understand and operate any systems your aircraft provides: gps, autopilot etc.

Proficiency of both should be practiced in order provided above, former being necessary for survival, and latter providing ease of operation and extra safety when used properly. I won't give examples of ratio between practising 1 and 2, as this varies hugely from one person to another.
As long as you are able to take over from any system, the AP for instance, at any time, no-one should (probably will though) frown upon using it.

P.S. the best mindset for GA pilot is to consider every flight a training flight. Set more goals than just fly from A to B to A. The most dangerous GA pilots are the ones who know it all and therefore no longer need to practise. They are as good as dead.

In the non-student GA world, I would say not very often. Maybe 1 in 6 approaches as a guess and from personal experience. If a pilot is flying actual IMC, they may fly a coupled approach as a safety measure. Most non-commercial GA pilots will avoid flying actual IMC in most cases as a rule. Some will fly actual IMC, when the conditions are not too bad, to stay sharp. Others will only fly their required 6 approaches in VMC. Either way, they will mainly hand fly the aircraft for the sake of staying proficient. I’ll usually make sure to fly 1 of my 6 on autopilot.
As far as the videos mentioned, how many of them were from training flights? More emphasis will probably be made on hand-flying on training flights. The DPE on my Checkride required one approach be done using autopilot. All of the others were required to be hand-flown.
Then again, this is speculation on the general aviation community based on my little microcosm of it. The sample size is only in the dozens.


text:
Why is it still mandatory to land a plane without autopilot?
I know that there are runways in the world that operate CAT III where the pilot can land with autopilot. But why do most airports with ILS not allow automatic landing?

Landings are fun.

@DeepSpace I'm confused, sorry. I will correct the question. CAT III is what I wanted to say.

If an airport is in a location that only gets 1 0-visibility day every 2 years, there is no reason to install such a system.

Not allow, or not equipped for?  Those are two very different things.


text:
Why does the second floor of the Boeing 747 occupy only part of the plane?
Why does the second floor of the Boeing 747 occupy only part of the plane, while the second floor of the Airbus a380 occupies the entire space of the plane?

Does this answer your question? Could the Boeing 747's 'hump' be improved aerodynamically?

The suggested dupe does not address the question, why not extend the hump farther back. There may be a question on here that answers that, but the suggested question isn't it.

The basic design of the Boeing 747 was originally developed to for the US military's CX-HLS program for a large cargo aircraft. One of the main requirements of the program was for cargo to be loaded from the nose, and placing the cockpit above the main cabin made this possible. The Lockheed C-5 Galaxy was selected, but Boeing carried the same features over to the 747.
In the 1960s when the 747 was being developed, some believed that supersonic aircraft would be taking over the long-haul travel market. The relatively short "hump" was retained not for extra passenger capacity, but so that if the passenger market dried up, they could keep producing the aircraft for the cargo market.
Boeing did extend the "hump" further back to add capacity on passenger versions, first on the 747-300 (and later retrofitted to a few -100 and -200 planes), and again on the 747-8I. Extending the second deck all the way back would create too many major changes to the structure and aerodynamics of the airplane, essentially making it a completely new model. Boeing did study a full double-deck model to compete with the A380, but opted to focus on a smaller, more fuel-efficient market with the 787 instead.

Wow, I would never have thought they would actually change existing planes to extend the upper deck. This must have been massive work...

In particular, Boeing was among the people who believed the supersonic aircraft would be taking over the long-haul market. They were developing the Boeing 2707 at the same time as the 747.

According to Joe Sutter, the chief designer of the 747, his team came up with the concept of a wide body as an alternative to a double decker. More efficient use of the available volume, and faster emergency egress. It took some selling, and several mockups, to persuade Pan Am to accept this new and radical design.
The 747 was initially conceived a stopgap effort in the mid 1960's, expected to be overshadowed by the 2707 SST under development. As such, it was modified for use as a cargo aircraft, by moving the cockpit above the main cabin, to facilitate a front opening nose for rapid cargo load/unload. The thinking was - when the 2707 came out, they could still use the 747 for cargo, where high speed wasn't required.
The fairing was added behind the cockpit for aerodynamics, and the extra space used for passengers. Originally, Sutter's plan was to have crew quarters there, to which Juan Trippe of Pan Am replied - Hell no. We're putting paying passengers there.
When the SST was abandoned due largely to skyrocketing fuel costs, the 747 was front and center as the first large airliner to make use of the more efficient high bypass turbofans, lowering fuel usage at a time when fuel costs had gone through the roof.
Why didn't they extend the upper cabin through the entire fuselage, as the A380 did?
The requirement for 400+ passengers from Pan Am was met by the widebody design.
Remember that when the 747 debuted, the typical international airliner (707, DC8) carried 150 passengers. So it was already a huge leap. Even more would have stretched the engineering challenges considerably, when the customer wasn't asking for that.

"Originally, Sutter's plan was to have crew quarters there, to which Juan Trippe of Pan Am replied - Hell no. We're putting paying passengers there." To be fair, the crew quarters (for the flight crew) are there, too, between the flight deck and the passenger cabin.

Fascinating posts here.   I bet the marketing idea that the upper deck is superior, super first class, played in to things over time too.

Was the SST really abandoned due to fuel costs, or was it because few countries would let it be flown supersonic over land?  After all, at that time air travel was pretty much limited to the prosperous, thus the term "jet set".

In the end, the Boeing SST was abandoned due to fuel costs. Arguably, it was also abandoned because it was too ambitious: Mach 3 with swing wings. When supersonic airliners were conceived in the early 60's, jet fuel was in the $.30/gallon range. Calcs were a 25% rise in fuel prices would make it too expensive to operate. After 1973, fuel costs went up by over 100%. The Concorde came out because most dev was paid for by 1973... it was a prestige item, but not economically successful. No orders outside of two flag airlines, and it never returned the dev costs, let alone a profit.

The 747's cockpit was raised for a different aviation market.  The "hump" was extended aft to improve its aerodynamics.  Back then a dual-deck airliner was being considered to maximize passengers, but it would have been too heavy.  But that was no longer the case for the A380.


text:
Is the FF (Fuel Flow) the fuel consumption index?
I am creating a program to calculate the fuel needed to fly and I need to know the fuel cost of the plane. In the boeing 737-800 (PMDG), on the display that shows the plane's systems, there is the FF (Fuel Flow) field. I think that is the fuel consumption index.

However, using a stopwatch, the value there appears to be incorrect. Advancing the throttle to keep the FF at 5, about 10 pounds was spent in 8 seconds. I expected 10 pounds to be spent in 2 seconds (5 pounds * 2 seconds = 10 pounds).
My question is: does the FF indicate the plane's fuel consumption? If so, does it indicate pounds per second? If not, how can I know the fuel consumption?

Timing anything for 10 seconds & then extrapolating that rate out to "per hour" values can induce lots of error in your observed values. Timing for a minute or longer will reduce the errors.  Plus, easy math, fuel used in 1 minute x 60 gives fuel consumption rate per hour, which is what your FF indications represent.

Why is there, in the picture, so much fuel in the centre tank and so little in the wing tanks? Shouldn't you always burn fuel from the centre tank first?

@JanHudec that is a random picture I've found on web just to show the Engine Display and the FF field. And that is the Engine Display of FSX's Boeing 737. It has a limit of about 8600 pounds in the wing tanks.

The FF value can show either the fuel flow or the fuel used, depending on the position of a switch on the center forward panel. If it shows the fuel flow rate, then the value shown is in thousands of kilograms or pounds per hour per engine.

1 FUEL FLOW Switch (spring-loaded to RATE)
RATE – displays fuel flow to engine.
USED –

displays fuel used since last reset
after 10 seconds, display automatically reverts to fuel flow.

RESET –

resets fuel used to zero
displays fuel used for 1 second, decreases to zero, then displays fuel flow.

2 Fuel Flow (FF) Readout (digital)
[Option - kgs] Displayed (white) – fuel flow to engine with FUEL FLOW switch in RATE
position (kilograms per hour x 1000).
[Option - lbs] Displayed (white) – fuel flow to engine with FUEL FLOW switch in RATE
position (pounds per hour x 1000).
3 Fuel Used Readout (digital)
Displayed (white) – when FUEL FLOW switch moved to USED or RESET.

(Boeing 737 NG FCOM 7.11.13 - Engines, APU - Over/Under-Displays)

With the wing tanks showing 84xx quantity, that's lbs rather than kg, so I'd assume that Fuel Flow is in PPH (x 1,000) rather than in kg/hour. Unless you've just pushed the Used/Reset switch to Used, the FF is showing flow. So, 99.8% of the time, it's displaying fuel flow.

@RalphJ Yes, it even says "FUEL LBS" in the image in the question, so that is in lbs. I just mentioned the kg for completeness.


text:
Three endorsements before solo?
Before a solo flight is allowed for a student pilot, what endorsements are required in continental USA?
Thank you!

This looks like information that could be found rather easily on google

Or in the FAR/AIM in the US.

You don't specify jurisdiction, but in the US, 14 CFR 61.87(n) specifies only one logbook endorsement required for a student to solo.

This sounds like quiz time, with the question based on an unassailable statement of fact.  If you have knowledge that 3 are required then cite your source.  Otherwise I agree with Gerry that only 1 is required.  (The question could be improved by simply asking "if" 3 are required...)

P.S.  Most flight schools will have a stage check, with a second opinion endorsement by another CFI, but this doesn't mean that it is an FAA requirement to have multiple endorsements.

Eenie, meenie, mynie...  if four were required, we could also bring in moe.

When you ask about regulations, please always tell us which country you're asking about. Even if it seems obvious to you, it may not be to others.

My answer will pertain to your first (presumably) local solo. You will need the following endorsements:

TSA Citizenship Verification: Title 49 CFR Part 1552.3(h)
Pre-Solo Aeronautical Knowledge: Title 14 CFR Part 61.87(b, c, & d)
Pre-Solo 90 day (local flight and limitations): Title 14 CFR Part 61.87(n)

@Michael Hall - Darn it. I meant to phrase those in the form of a question, Alex.

Item 1 should be 49 CFR 1552.3(h) for "U.S. citizens and nationals and Department of Defense endorsees."  It requires the student to provide the documentation and sub paragraph (i) requires the school to maintain a copy for 5 years.  It does not specify a logbook endorsement.

@Gerry - thanks. Changed 14 to 49. I received two in my logbook. One from a fixed wing school and one from an rotary wing school unaffiliated with the fixed wing school. I’ll have to look up the actual Reg.

The knowledge test and training in 61.87(b...m) must be documented (written test, flight training logged) but there's no separate endorsement required. The instructor must verify it before providing the endorsement specified in (n) or (m) (for night solo). I actually had several endorsements, but they were driven by school policy. The first had wind, crosswind, visibility and 'local area' restrictions.  Later endorsements raised the limits.

@DeanF.  49 CFR Part 1552.3(h) only pertains to flight schools, not private instructors.

There is no requirement for multiple endorsements.  Title 14 CFR 61.87 spells out the requirements for student solo flight.  There are many requirements, but the question was  about endorsements.
61.87(p)(4) is the only part of this section that specifically addresses endorsements, and it says:

(p) Limitations on flight instructors authorizing solo flight. No instructor may authorize a student pilot to perform a solo flight unless that instructor has -
(4) Endorsed the student pilot's logbook for the specific make and model aircraft to be flown, and that endorsement remains current for solo flight privileges, provided an authorized instructor updates the student's logbook every 90 days thereafter.

As long as the CFI verifies all requirements of the section are met, only one safe-for-solo logbook endorsement is needed.


text:
Can a fixed-wing plane jump up by blowing air over its wings?
NASA's X-57 electric plane has 12 wing-mounted propellors which drive air past the wing.
This video describes how the resulting increased air velocity causes an increase in the amount of lift the wing generates.
Suppose the propellors could generate enough airspeed over the wing to lift the entire plane -- could the plane then jump into the air without needing a runway?
This would require that sufficient lift is generated before the propellor thrust (minus wing drag) exceeds the craft's friction with the ground -- otherwise the propellor thrust would push the craft forward some before a liftoff could occur. And that leads to my secondary question: Is blowing air over a wing a more efficient means of achieving lift than would be directing those propellors downward rather than laterally over the wing?

You're talking about something like the Custer Channel Wing?

Related: Could a blown wing ever be powerful enough to lift an aircraft at zero forward velocity?

Isn't this a kite?

The Hummingbird is (was, the page hasn't been updated since 2011) a concept for an aerobatic plane with a big ol' ducted fan in it. The plans say that it could be capable of VTOL. Some RC Models were made but I don't think they were VTOL capable.

"the resulting increased air velocity [from the engines] causes an increase in the amount of lift the wing generates." is how planes fly, no? Except for gliders.

@user253751 Not exactly. Usually, the propellor pushes or pulls the aircraft along, and then because the aircraft is moving, there is airflow over the wings, which generates lift. The propellor isn't causing the airflow over the wings directly; most of the air from the propellor doesn't touch the wings, and most of the wings are untouched by prop wash. (For an extreme example, look at a pusher prop, where all of the propellor's airflow is behind the aircraft, not touching any of it.)

Yes, a strong enough airstream can lift the plane. Problem is, the moment it's off the ground,  that airstream will blow the plane backwards as well as upwards.  There's no equivalent of a sailboat's keel.

Isn't this why we tie our planes down when we park them?

https://www.opener.aero/

As a partial answer to your question, air moving over a stationary (relative to the ground) wing will generate lift. There have been several weather related incidences where aircraft were picked up off the ground by significantly strong winds. Videos of these incidents showed that it was lift and not force from form drag that lifted the aircraft off the ground. In the case that the planes were tied down, they would come back down to earth in place. Unfortunately, the force of the decent, in some cases, was still enough to damage the planes.
I am uncertain about what you mean by “This would require that the lift generated would exceed ground friction reacting the propellor thrust...“. Lift would be acting roughly perpendicular to the wings chord line, and the plane’s longitudinal, and lateral axes. On the other hand, any friction created by the relative wind would be acting roughly parallel to the relative wind and the plane’s longitudinal axes. The only ground friction would be that caused by the wheels touching the ground.
Thrust is a function of Newton’s Laws of Motion. The propellers turn chemical energy (in this case electrical energy) into thermal and mechanical energy. The mechanical energy is used to accelerate a mass of air. The mass of the air is accelerated by the propellers creating force. This force acts on the mass of the airplane to accelerate the airplane. The relative wind created by the propellers would act upon the airplane in the form of thrust and upon the wings to create lift regardless of how close to the ground the airplane was.
P.S.
Edited to include a new link pertinent to the discussion. Here is a new VTOL aircraft soon to be on the market.
Blackfly

Thank you for the response. I've rewritten part of the question as I realize my original wording did not make sense. The friction I meant to speak of was between the aircraft and the ground, which would be reacting to the propellor thrust (not lift), and the question I meant to ask was whether sufficient lift could be achieved without propellor thrust (minus wing drag) exceeding that ground friction.

@mherzl - Ah. Maybe. This is definitely a mathematical question. In a normal airplane, the propeller slipstream acts on such a comparatively small part of the wing’s surface. The thrust of several propellers along the wing would contribute much more slipstream to the entire system even if the combined thrust were equivalent to a normal plane. You can see the aerodynamic differences in current single engine versus multi-engine planes.

It's "force of the descent", not "decent".  If the descent is indecent, there may be an incidence of damage.

Not sure if this is on point, but there are a few videos on youtube of parked unmanned aircraft lifting off in high winds - they weren't tied down, and off they went.  They lift and kind of get blown backwards - probably flip over and get wrecked.
Its the relative speed of the air going over/under the wings that generates the lift - how that relative velocity is achieved (propeller thrust or wind) is irrelevant. So to answer the question, yes, if you blow hard enough.

And this phenomenon isn't limited to airplanes; the same thing happens to tents, canopies, trampolines, etc.

And of course, kites and specialised gliders make use of it. The important thing is a tether to the ground!

(I am not a pilot, but...)

This would require that sufficient lift is generated before the propellor thrust (minus wing drag) exceeds the craft's friction with the ground -- otherwise the propellor thrust would push the craft forward some before a liftoff could occur.

The friction between two things is proportional to the force pushing them together - that is, weight minus lift. When lift equals weight and the plane can start moving upwards, the friction force is zero. Some time before that, the friction is less than the thrust.
So, no, you cannot take off vertically with horizontal thrust because at some point before the lift exceeds the weight, the thrust will exceed the friction.

Although your answer provide useful information, I fail to see how it answers the question. I think it should be a comment so that the OP can improve its question.

@ManuH The answer to the question is "no".

your answer only address ground friction. This does not cover possible short or vertical takeoff

@ManuH You cannot take off vertically with horizontal thrust because at some point before the lift exceeds the weight, the thrust will exceed the friction. As I just said.

@ymb1 Now the answer says the same thing twice.

@user253751 - The point is still made. Truly vertical take off relative to the wind will not be achieved. There are scenarios where vertical take off relative to the ground can be. For instance, in calm wind, the aircraft will start moving in the opposite direction of thrust as soon as enough weight is lifted from the wheels. If the aircraft were tethered, this would not be an issue. If the aircraft were facing into the wind, at some point thrust and drag will be equal, causing no motion or acceleration. This would also aid in lift, requiring less thrust to be required from the propellers.

The variables in the lift equation (below, from wikipedia https://en.wikipedia.org/wiki/Lift_(force)) are the density and velocity of the air flow. How the air reaches that velocity is not relevant to the amount of lift generated.
$L={\tfrac 12}\rho v^{2}SC_{L}$
where
${\displaystyle L}$ is the lift force
${\displaystyle \rho }$ is the air density
$v$ is the velocity or true airspeed
$S$ is the planform (projected) wing area
$C_{L}$ is the lift coefficient at the desired angle of attack, Mach number, and Reynolds number


text:
Hood time with an autopilot
I'm trying to build simulated instrument time (under the hood) flying an airplane with an autopilot.  Let's say I have a safety pilot, I put a flight plan in the autopilot, I put the hood on, I engage the autopilot, and let the autopilot fly the plane for an hour on the flight plan while I monitor the autopilot with the hood on, and I don't touch the controls.  Can I log an hour of hood time, and also PIC time?  Would I be the sole manipulator of the controls even if I'm not touching the controls?  It seems strange, but it seems like I should be able to log the time.

Yes, you can log the time as both PIC and simulated instrument. The Murphy interpretation discusses this:

The FAA considers a pilot's use and management of the autopilot to be the equivalent of manipulating the controls, just as one manages other flight control systems, such as trim or a yaw dampener. The autopilot system's sophistication does not affect a pilot's responsibility to manipulate and manage all control systems, including an autopilot, appropriately. Therefore, a pilot may log PIC flight time as the sole manipulator of the controls for the time in which he or she engages an autopilot.

Note that this means that you must be the one to do any required manipulations to the autopilot. If your safety pilot does them, they become the sole manipulator of the controls. And though you say "I don't touch the controls," you can't really know that beforehand. If the autopilot starts doing something funky or there is a traffic conflict you need to be ready to override it.

Of course if you are under the hood and the autopilot gets funky then you can come out from under the hood.

@DJClayworth You could. But dealing with it under the hood is much more valuable from a training standpoint. If the autopilot gets funky in actual IMC you can't just turn off the clouds.


text:
What altitude restrictions are there in Class C airspace?
So if I'm flying into a Class C airspace, I call approach and I establish radio contact and tell them I want to land, then I enter the airspace.  If I'm still talking to approach and haven't been handed to tower yet, and they tell me to make (say) left traffic for Runway 15, does that give me permission to descend to TPA?  When do I need to maintain a specific altitude in Class C and when can I descend at my discretion?  And more broadly, if ATC doesn't give me any altitude restrictions in the Class C, can I fly at whatever (safe) altitude I want to as I come in for the landing?

I added the faa-regulations tag on the assumption that you're asking about the US. If that isn't correct, please tell us which country's regulations you mean.

To correctly answer this question we need more information. At the very least we need to know if you are operating this flight under IFR or VFR; whether you are flying a turbine powered aircraft or not (i.e., does 91.129/130 apply).

Absent an explicit instruction to the contrary, VFR traffic can do whatever it wants in class C/D/E airspace. ATC is not supposed to give you both lateral and vertical control instructions at the same time because that could interfere with your ability to maintain VFR cloud clearance requirements. Class B has different cloud clearance, so you will almost always get both, and you should "unable" them if complying is not legal.
If ATC has told you to "advise any altitude changes", then do so—before starting up or down. If they told you "altitude your discretion", then they don't care. If they said neither, it's recommended to advise by default unless you're doing something where an altitude change is obvious, such as entering the pattern. They key is to not surprise them.

This is incorrect insofar as turbine aircraft are required to comply with certain minimum altitudes in Class C airspace as required by 91.130 regardless of VFR or IFR operations. This answer appears to be true only for piston aircraft.

@J.Walters I didn't address 91.119 either since it's not relevant to the OP's question.

Perhaps I stated my point poorly. In class C airspace large and turbine aircraft are required to maintain at least 1500 ft AFE until further descent is required for landing. Thereafter, with certain exceptions, such aircraft must not descend below vertical guidance until DA/DH. VFR traffic—as a category—are not permitted to merely do as they wish in class C airspace when altitude is concerned.

@JWalters I read Stephen's answer as describing what rules or expectations ATC has for VFR pilots in Class C airspace. Of course the pilot should be familiar with 14 CFR and conduct their flight in accordance with all applicable regulations (which ATC does not enforce).

@Randomhead Specifically in response to the question "And more broadly, if ATC doesn't give me any altitude restrictions in the Class C, can I fly at whatever (safe) altitude I want to as I come in for the landing?" the answer is "No", as I detailed.


text:
How was it possible in the 2000's for two pilots on an international passenger flight to be so poorly trained (AF 447)?
Looking at the cockpit recorder transcript from AF 447, two things seem clear to me:

The two pilots flying (not the captain) did not know very well how to steer the airplane up and down, if the autopilot is down.   It seems to me, flying the aircraft manually, in particular, up and down, should be the first thing they learn in flight school.

All the pilots did not logically communicate and follow procedures for management in the cockpit. In particular, two pilots attempted to control the same aircraft functions at the same time, which seems, should be the first thing they learn in flight school, about cockpit communication, not to do.

(please correct me if my opinions are clearly incorrect).
How was this possible on a big flight on a big airline in the 21st century?
Should I assume that:

In AirFrance, in 2009, a substantial portion of pilots, did not know such fundamental things?

Or is true for most airlines?

Or maybe AirFrance did not pay critical attention to hire pilots who can perform well under great pressure, which it seems to me should be a fundamental requirement for a pilot (to not forget everything when the shit hits the fan)

If if any of this is true, did AirFrance (and perhaps others) make fundamental improvements to their hiring and/or training after this accident?
Thank you

Read the official report. It makes a number of wide ranging recommendations regarding training.

@CatchAsCatchCan Do we know that AirFrance followed them? As far as I know, AirFrance never even admitted their training was deficient in any way.

I'm voting to close.  This calls mostly for an opinion, and very few are qualified to accurately critique their actions.

@Mark I don't know, but I'd assume that if they didn't then EASA would have something to say about it.

@MichaelHall yes, but opinions of experts on this site, carry the weight of being most likely true.  Aviation is not an exact science like mathematics, everything is an opinion to some degree, and experts opinions are just about as good as absolute truth.

I was actually mostly expecting the following answer to my question: Mark, thank you for the question, but you are obviously incorrect, because ... , don't worry, AirFrance is a fine airline and would never do such a thing...

please correct me if my opinions are clearly incorrect While opinions are by definition not correct or incorrect, you present the facts in the least constructive way possible. Yes, stall recovery and CRM training were evidently not effective in preventing this particular accident, but that's a whole different league than "flying the aircraft up and down". -1 from me for reducing a complex topic to basically a childish insult.

@Sanchises As a non-aviator, I tried my best to make the question simple and to the point. What seems to you like an insult from the point of view of an expert, is actually a normal understanding of things from the perspective of a non-aviator

Downvoted. Read the report, crew is far from the only cause of the accident.

@MarkGaleck 447 is best seen as a kind of perfect storm of elements that came together to create chaos.Use of "cruise pilots" to allow crew to rest. An event that nobody anticipated and nobody trained for because the phenomenon was poorly understood. Two inexperienced pilots, one of whom was perhaps at the left edge of the bell curve in terms of fundamental skills and instincts and went into brain lock right away, which ended up also overloading the other one. You sim train, but never know how you'll do with the real deal. When the real deal is an event from total left field, all bets are off.

Admittedly, I came away from reading the accident report thinking exactly the same. My past experiences with that airline let me avoid it like the plague, and AF447 is only one in a long list of reasons.

@Mark Galeck, you may have tried your best, but this reads like a rant seeking validation.  There is a time and audience for dispassionately analyzing the final actions of men whose mistakes cost them their lives, and critiquing the training and airline culture that may have contributed to the tragedy, but this is not it.

There are two factors at play:

The training at the time, not just in Air France but worldwide, was somewhat lacking. Airline pilots were given training on stall prevention with a strong focus on minimising height loss, so a somewhat timid and gentle manoeuvre. But there was very little focus on actually recovering from a fully developed stall.

Pilots of light aircraft receive such training, but the stall characteristics of large swept wing aircraft are much different and so too is the recovery procedure - in a light aircraft you generally firewall the throttle, but doing that with big powerful jet engines can worsen the situation due to a strong pitch up effect.
Probably the biggest development arising from this accident is the introduction of Upset Recovery Training, or UPRT. This training exposes pilots to the recovery from extreme situations including stalls.
Now, even without UPRT training, the AF447 pilots probably should have been able to recover the situation if they could have properly understood what was happening. However:

Pilots are human beings, and human beings cannot reliably perform under extreme stress 100% of the time. If you expose them to these (simulated) emergencies often, the pilots will have hopefully built a "muscle memory" to revert to when the real thing happens. But, sometimes all the training in the world can't overcome the human freezing up, as the relief first officer in particular did.

To your question:
"If if any of this is true, did AirFrance (and perhaps others) make fundamental improvements to their hiring and/or training after this accident?"
As regards the Training aspect, here is the Foreword to the ICAO Doc 10011 -
"MANUAL ON AEROPLANE UPSET PREVENTION AND RECOVERY TRAINING". This was published in 2014, after a landmark study by all major players, and is a direct result of 447 and other such accidents. Implicit, is recognition that there was a gap to be filled, but not just for the 2 pilots, or a particular airline.

FOREWORD

Between 2001 and 2011, aeroplane accidents resulting from a loss of control in flight (LOC-I) event were the leading cause of fatalities in commercial aviation. LOC-I accidents often have catastrophic results with very few, if any, survivors.

Following a conference in June 2009 on aeroplane upsets and loss of control in flight, the Royal Aeronautical Society (RAeS) initiated a study to investigate the LOC-I phenomena and make recommendations on mitigating strategies, notably with respect to potential improvements to international civil aviation standards and guidance material. This work was undertaken by the RAeS International Committee on Aviation Training in Extended Envelopes (ICATEE). ICAO supported this initiative.

In 2011, the Federal Aviation Administration (FAA) of the United States of America commissioned an aviation rulemaking committee (ARC) to develop effective upset prevention and recovery training methodologies. In 2012, ICAO, the European Aviation Safety Agency (EASA) and the FAA decided to combine efforts to identify and establish an acceptable approach to reduce such occurrences. ICAO sponsored seven meetings in 2012 during which Civil Aviation Authorities (CAAs), the FAA ARC and subject matter experts were encouraged to participate in focused discussions. Also, as several initiatives were underway simultaneously that sought to reduce the number of LOC-I events, ICAO brought many of the groups involved with these efforts into the ensuing discussions under what became known as the loss of control avoidance and recovery training (LOCART) initiative.

Reducing the number of LOC-I accidents is an ICAO priority, and ICAO has developed harmonized training requirements for flight crews that address and mitigate LOC-I events. Supported by ICATEE and the FAA ARC, ICAO has introduced improvements to existing Standards and Recommended Practices (SARPs) and corresponding guidance material. Both on-aeroplane training at the commercial pilot and multi-crew pilot level and training in a flight simulation training device at the airline transport pilot and type rating level are now promulgated in Annexes 1 — Personnel Licensing and 6 — Operation of Aircraft, Part I — International Commercial Air Transport — Aeroplanes, as well as in the Procedures for Air Navigation Services – Training (PANS-TRG, Doc 9868,), with an applicability date of 13 November 2014. This manual provides guidance to support these new provisions and is only applicable to the training of aeroplane pilots.

The content of the manual was developed over a period of three years with input from many groups of experts from aircraft and flight simulator manufacturers, pilot representative organizations, airlines, training organizations, accident investigation bureaus, human performance specialists, etc., and was thereafter submitted for an extensive peer review to collect and take into account comments from the expert community. It is based upon the latest forms of technology available at the time of its publication. As such, it will be subject to a revision process that will be governed in large part by changing dynamics within the industry. Comments on this manual, particularly with respect to its application, usefulness and scope of coverage, would be appreciated. These will be taken into consideration in the preparation of subsequent editions. Comments concerning the manual should be addressed to:

The Secretary General
International Civil Aviation Organization
999 University Street,
Montréal,
Québec H3C 5H7
Canada

I hope this brings a better perspective.


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Controlling a plane only by shifting weight
Suppose that a plane lost the ability to use all the control surfaces on the wings (e.g., flaps and ailerons). Can the weight inside the plane be shifted to help maneuver the aircraft?
For example, moving passengers side-to-side in order to turn, or between the front and back to climb or descend.

related: https://aviation.stackexchange.com/questions/1659/is-passenger-weight-distribution-important-on-a-commercial-flight?rq=1

It works for hang gliders.

Assuming you mean no roll control at all, lateral weight shifting has an effect too mild to be able to achieve useable control.
However, most airplanes can be controlled in roll by yawing them, depending on how strong the design's dihedral effect and roll/yaw coupling is.
For example, high wing Cessnas that have geometric wing dihedral along with the T wing placement can get decent roll rates going just by skidding. I used to tow gliders in a Cessna L-19 and I could control the plane reasonably well just with trim for pitch, and rudder for roll, without touching the stick at all, and I could probably land it in one piece, or at least walk away from the result, using trim and rudder only, if the runway was long enough.
Swept wing jets have very strong dihedral effect from the wing sweep itself (so much that anhedral is required if the wing is on top, to reduce total dihedral effect). If you lose all aileron control in a swept wing jet you can get very high roll rates going with small amounts of rudder-induced skid. As long as the yaw damper is still working so you don't have to struggle against dutch roll tendency, you could maneuver a jet around with mild rudder inputs to skid it to roll it into a bank, if you were very careful, if you had no aileron control (I used to experiment with that in the CRJ simulator, just for fun).
Landing a jet on rudder alone, well I'd try it if I had no choice, but I'd probably crash it.

could putting all the passengers on one side turn the plane? +1

Yes you'd get a very mild roll (there are lateral Center of Gravity limits related to trim authority), but you'd have to order them all back and forth and the roll rates you get aren't enough to achieve anything more than very gentle maneuvers. The rates you get with gentle skids is WAY more. That's what I meant by "too mild to be able to achieve useable control".

In early swept wing jets, when at high AOA, (as in landing), we only used the rudder/sideslip to roll. Aileron input would create adverse yaw, opposite roll and loss of control, (google "Sabre Dance" to see the result). Until they added leading edge slats to the F-4E, we only used the rudder when landing.

Was there a tendency to excite dutch roll?  The CRJs are stable in dutch roll mode when flaps are extended and you could control it with rudder even with yaw dampers off. It sounds like the F-86 was like that.

As explained in the other answer, most aircraft are too stable for sideways shifts in CG to induce a useful roll.  That answer does a great job answering the question in your text.
However, your title question seems more general.  Most hang gliders are entirely controlled by shifting the CG.  So it is possible to entirely control an aircraft by CG shifts.
I also recall a report of a pilot of one of the Horton flying wing gliders (with very little sweep -- a 'flying plank') was able to loop the aircraft by nodding their head forward and aft.

There are also ultralight powered aircraft that manoeuvre this way as well; in some areas, they're called "microlight aircraft".


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How does a transonic aircraft gains longitudinal stability
How is the transonic aircraft lift augmentation help in achieving stability

Does this answer your question? How is an aircraft designed to be longitudinally stable? If not, please tell us exactly what extra information you're looking for that isn't already covered in your previous question.

I second @Pondlife, I bet there is a good question in the making here, just needs to be set up more specifically. What is it you do not understand in the longitudinal stability at transsonic speed?

I would like to know how is it achieved?


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Why do we feel negative G-forces in a high speed descent in a pressurized aircraft cabin?
Could different momentums affect g-forces differently?
The way I see it, as an object accelerates, G-forces begin to be produced. As speed increases continuously, G-forces increase. When speed is constant (at any speed), no g-forces are created.
Am I looking at this correctly? What is not right, and what am I missing?

Comments are not for extended discussion; this conversation has been moved to chat.

There are two misconceptions here, lets sort them out first:

pressurization has absolutely no effect on G -forces. For any maneuver they will be exactly the same, wheter you are in a pressurized, unpressurized, or even an open cockpit or passenger compartment.

G forces other than the normal G can only be felt (or registered) when there is a change in the trajectory of a plane (or any object), and only during the change

So: when beginning a descent, the plane's trajectory must be changed by pointing the nose down (well this is a simplification, but lets just go with that). For the brief moment it takes for the plane to reach a steady descending speed, a reduced G can be observed. As soon as the descending speed becomes steady, the G-force is back to normal.
What a passenger might interpret as negative/reduced G, is the effect of the vector of gravity pointing slightly forward, as the plane's nose is pointed down, so "the seat of the pants" is telling us there's something fishy going on.
The difference to simply sitting on a chair tilted forward is that in a descending plane the whole close proximity surroundings are also tilted, making the brains think things are level when they actually are not. As the brains are accustomed to "calculating" G forces as always pointing straight down, input from your body computes the G force being less than normal.

It’s probably worth noting them at “G forces” in most cases (and most definitely here) have nothing to do with gravity, only acceleration. They are just expressed in terms of gravity because that’s something people can more easily relate to.

Yes. 1 G is the gold standard of how much the crust of the earth resists us and the earth from merging

Einstein developed his theory of General Relativity based on the principle that inertial mass and gravitational mass are one and the same thing. When your plane accelerates, you therefore feel a G force according to the Newtonian equation F = ma.
If you want to understand more about the consequences of Einstein's principle and why we all accept it, you will need to get to grips with tensor calculus, Minkowski space and curved spacetime.

Oh man you jumped straight into the deep end

@Jpe61 How deep is "because it is accelerating"?

Oh not that, dropping in Minkowski space and tensor calculus is. Even Einsteind had trouble with tensors

@Thomas check this out for a crash course on Albert's and Isaac's ideas on stuff: https://youtu.be/AwhKZ3fd9JA

The short answer is that we do NOT (under "normal" conditions) experience negative G forces in a descent.  The speed makes no difference, nor does pressurization.
There are some excellent answers already, but I would like to offer my perspective to help ensure complete understanding.  Let’s keep it simple, and discuss only 1G, 0G, and -1G.  And let’s keep it earth bound to start.
1G Surface:  Everyone alive knows what this feels like, it is the force of gravity from the earth.  Our entire physiology is adapted for life at 1G.
0G Surface:  This is weightlessness.  We only sort of experience this swimming in the water, or jumping off something high.  In the water, your natural buoyancy simulates zero gravity, but it doesn’t have a good comparison in the air so let’s ignore this example.  When you jump off something high, however, your body will begin to accelerate downward at 32ft/sec squared.  Because this free fall acceleration rate effectively cancels out the 1G feeling you get when the earth opposes your motion, you experience this weightless acceleration as zero Gs.  (This is relevant to flying, which I will get to...)
-1G Surface:  There really isn’t such a thing as negative G force on the surface because the earth doesn’t repel you, but when you hang upside down your body will experience the effect as negative 1G because gravity is acting opposite to the normal orientation of your body’s vertical axis.  Because we are adapted to having the force of gravity pulling towards our feet, the blood will rush to your head, and breathing and swallowing will become more difficult.  If you have never hung upside down from a tree branch as a kid, try it.  This is what -1G feels like.
Now let’s consider these same three examples in the context of what our bodies experience while airborne.  To keep things simple, let’s disregard high performance aerobatic airplanes and military jets, and focus only on “normal” passenger flights.  Our starting point is upright straight and level flight, (balanced unaccelerated) flight.
1G Airborne:  This is what you normally feel as a passenger in smooth air when all forces on the aircraft are in equilibrium.  You will also feel 1G in a climb or a descent because the forces are in equilibrium, just like you will feel 1G in your car whether you are driving up or down a hill.  You will only feel a momentary very slight increase in G when beginning a climb, or a slight decrease when initiating a descent, then it will even out.
0G Airborne:  Presuming your starting point is straight and level flight, (i.e. not trying to fly a parabolic arc) if you experience zero G airborne it is because you are accelerating towards the earth at the speed of a free falling object.  Quite literally, falling like a rock.  This can be accomplished by a pretty aggressive push forward on the controls, but can only be sustained by any airplane for a few seconds until reaching an extreme nose low position and exceeding the airspeed limit of the aircraft.  Beverages and food would "float" up in the air, and your whole body would feel weightless in the seat.  So, it shouldn’t be difficult to realize that passengers don’t experience sustained zero G in normal flight.
-1G Airborne:  While I specifically excluded aerobatic aircraft, it is worth noting that if you are flying straight and level but upside down, (inverted...) your body will experience one negative G, hanging from your seatbelt just as if you were hanging upside down on a playground.  But upright it is a far different story... If you experience -1G from a straight and level upright start it means you are accelerating towards the planet at TWICE the rate of a free falling rock!  Your drink would fly up in your face, you would be pulled towards the ceiling and feel like you were hanging upside down.  Anyone not seated and strapped in would be pinned against the top of the cabin by a force equal to their body weight.  Again, this can be sustained for mere seconds before being in very dangerous steep dive and reaching an airspeed that would rip the airframe apart if not corrected.  So, it shouldn’t be hard to see why I challenged your presumption in the question that passengers experience negative G during a descent!
The only time a passenger should experience zero or negative G is very briefly in moderate to severe turbulence.
Disclaimer:  There may be some physics majors who will have things to say about my examples.  I welcome your feedback, and will edit my answer to make it better, but the intent is to provide practical and relatable examples, and not turn this into a math lesson...

Comments are not for extended discussion; this conversation has been moved to chat.

@Fargan... do you know what the most negative part of this Site is?

The negatives Gs we experience reading your comments?

What you are calling G-force is not really a force. And, it does not really have anything to do with gravity. It is simply what you feel when you accelerate. It is called G-force due to the fact that it is equal to the amount of acceleration one would experience due to the force of gravity at the Earth’s surface (1G = 9.81 meters per second per second).
Acceleration occurs when an object has a change in the magnitude (amount) of its velocity and/or has a change in the direction of its velocity. If both the amount and the direction of an object’s velocity does not change, and remains steady and constant, there is no acceleration. If there is no acceleration, there is no G-force.
That being said, positive and negative, when it comes to Gs, is subjective and does not truly exist. We just call acceleration upward (relative to us) positive, and acceleration downward (relative to us) negative.
In the same token, when an aircraft banks to turn while keeping its altitude constant, we call it positive Gs even though the G-force is actually to the side, acting laterally and parallel to the Earth. And, an aircraft in a turn is continuously changing direction throughout the entire turn. So, you feel the “positive” Gs throughout the entire turn.
In a climb, you only feel “positive” Gs while the aircraft is accelerating or at the very beginning of the climb. Once the aircraft’s speed and direction have stabilized, you no longer feel “positive” Gs. The same is true in a descent. You just feel Gs in the opposite direction.
To use an analogy with which you might be more familiar, a car does the same thing.

When a car accelerates, you feel Gs to the back.
When a car decelerates or stops, you feel Gs to the front.
When a car goes around a curve or corner, you feel Gs to the side.
When a car goes down a hill, reaches the bottom, then immediately goes up another hill, you feel “positive” Gs downward.
When a car reaches and goes over the crest of a hill, you feel “negative” Gs upward.

In the car analogy, you are experiencing Gs even though the car is not pressurized. That is because pressurization has nothing to do with G-forces. And, just like in the car, you would feel similar G-forces in an aircraft regardless of if the cabin is pressurized or not.

Depending on theory, gravitation might not actually be a force at all.

@Dean I asked a question from Michael Hall as a comment under his reply above, I want your view as well thanks.

@Dean as your knowledge in aviation is 100 times more than me, could you help me and say how much steam and at what pressure is required to have 2KN of thrust for 20 seconds? I post it as a new question but was closed and said that not valid question for this forum.Thanks

@Thomas - Unfortunately not. Firstly, to answer that question several parameters would have to be specified. Secondly, I am not an experts at steam propulsion. You may need to know the size of the orifice or at least the rate of steam through the orifice to get you near an answer. Although, knowing the pressure may get you close. Just remember that F=ma. The mass of the steam would start at 0, then the steam would accelerate to a certain, yet unknown, speed to create the 2 kN of force. Since this is not an aviation question, it might be best posed on SpaceStackExchange.

@Thomas - By the way, you should probably limit your question here to those involving flight in the atmosphere, aircraft, airports, pilots, and aviation regulation. If you need help for a vehicle that leaves the atmosphere, this probably is not he forum for it. And yes, 30 or 40 kilometers is technically below the Karman Line, it is still above the level of conventional aircraft flight. Then again, traveling at Mach 10 is also beyond conventional flight. And, 2 kN (450 lbs) would not be enough to overcome drag and reach Mach 10 in a passenger aircraft. Even the X-43 is experimental & unmanned.

@Dean, ok I will never ask any more question. And I wonder from where you brought 10 Mach or those KM altitude, what is that? You may referring my previous comment days ago , if so, it had nothing to do with that. But as I like you I say that what I was looking for here was about a new technology and with most respect to all answers but I should say i failed to be successful here to get what I want.

@Thomas - I am sorry that you feel that way. Feel free to post as many questions as you like here. Just remember, this forum has protocols. Such as, questions here should not solicit opinions. They should be inquiries seeking actual answers that can be cited and referenced with verifiable facts from reliable sources such as the FAA or EASA. Also, limit the questions to those pertaining to flight, flight dynamics, aerodynamics, aeronautical engineering, piloting, aircraft maintenance, aviation regulations, anything to do with airplanes, etc.


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Why do most canards have swept wings?
So most canards have swept back wings. Now I have been told that it is that way to ensure yaw stability (for example in a crosswind) - not sure though.
But then I look at the new Lilium jet, which is a canard, but has straight wings.
What are the reasons for backswept wings to be so popular in canards then?
Also, what are the pros and cons of having the canard itself be swept back / straight ?

Would it not be more appropriate to ask why some swept wing aircraft have canards?

@CatchAsCatchCan are you implying that whether a canard-type aircraft has swept back or straight wings, the effect on yaw is nothing?

I'm not implying anything other than the use of canards arises from other more important requirements. The original concept drawings for the Lilium jet had no canards, and the machine wouldn't fly as a result.

@CatchAsCatchCan Alright but then my question still stands. Does having straight wings on a canard aircraft result in yaw instability (for example in crosswinds or gusts) ?

There are basically two categories of aircraft with canards:

modern European fighter jets (Grippen, Eurofighter, Rafale), and
many of Burt Rutan's designs

The fighter jets have delta wings because they are most appropriate for fast flight in the high transsonic and slow supersonic region (as these jets have supercruise capability). And the reason they have canards is that they are more efficient for pitch-unstable designs (aerodynamically unstable with computer stabilization provides faster control response), and double as vortex generators at high angle of attack, improving slow speed or high-G handling.
For Burt Rutan, well, he always liked doing thing differently than everybody else. Even if it usually was not the most efficient way, but he was good enough to make it work. But not all of his canard designs actually have swept wings.
The best known of his designs, the VariViggen/VariEze/Long-EZ line, uses swept wings. Here the reason is that he moved the vertical stabilizers to the wing-tips to make room for the pusher prop and avoid the weight of additional booms. And because it was inspired by the Viggen.
But he also made other canard designs like the model 77 Solitaire that has straight wings. And if you go through the list of his designs, you'll see most are straight wing, often either with canard or tandem wing (the surfaces are of comparable size and contribute similar amount of lift).

Regarding the stability: swept wings increase lateral stability (yaw-to-roll coupling), and the thing with that is that you don't actually want as much as you can get in a design, you want just the right amount. Otherwise you'll get strong tendency for Dutch roll. The stability can be adjusted most easily by changing the dihedral, so simply if the aircraft has swept wings, it ends up with less dihedral or even anhedral (as in most high-swept-wing designs as high-wing configuration also increases the coupling).
There is no reason to use swept wings because of canards, they don't affect lateral stability much. It is just that for the fighter jets it happens to be a good design point and for the VariEze it was part aesthetics and part other reasons.

Piaggio Avanti is actually a three-surface design ;-)

@sophit, right, … and the foreplanes are fixed, so they don't count as canards.

Anyway very good answer

Since you mention Rutan canards, what about the Quickie?

@StephenS quickie is one of the many other straight-wing designs.


text:
Which WW1 plane is this?
I have another scanned negative from my collection (see my other post with Emil Werner).
I just would like to know what kind of plane it is.

It sure looks like Werner Emil. Hard to be sure because we can't see all his buttons.

@A.I.Breveleri: note that it seems to be Emil Werner, not Werner Emil. Both "Emil" and "Werner" are German given names, but this gentleman seems to have "Werner" as his family name and "Emil" as his given name, and in German the given name comes first.


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Why do F-35B jets hover with their weapons bay doors partially open?
This is an interesting phenomenon noted for F-35B aircraft during vertical flight and vertical landing.  They will do so with their weapons bay doors partially opened.

Of interest, this only occurs during hover (ref 2:48 in the video above) but not in slow flight while the lift fan system is activated.
I have never found the reason why this is so. Does anybody know if Lockheed Martin installed additional auxiliary air intakes inside the weapons bays to provide additional air to the engine during hover?

Can you point at the time in the video where you observed this and/or provide a still image?

Only when landing on a ship, not when landing at an airport?

Somewhat speculative, as I have not (yet) found a fully authoritative source:
Partially open weapons bay doors create a channel that moderates the airflow from the nozzles as the aircraft comes closer to surface, creating a cushion of air between them.
The configuration is similar to AV-8B Harrier's Lift Improvement Device system (LIDs), which was developed to mitigate Hot Gas Ingestion (HGI) in close ground proximity.
I also suspect they limit the spanwise flow of air in the same situation. This flow would adversely affect the efficiency of the auxiliary nozzles in the wings, possibly compromising controllability.
This Youtube video shows the weapons bay doors opening as the aircraft is approaching for landing, note that the plane is already in VTOL configuration.

I wonder if for the same reason the landing gear compartment doors stay open even some time after the landing gear is stowed.